An ink jet printer of Liquid ink printers of the type frequently referred to as continuous stream or as drop-on-demand, such as piezoelectric, acoustic, phase change wax-based, or thermal, have at least one printhead from which droplets of liquid ink are directed towards a recording medium. Within the printhead, the ink is contained in a plurality of ink conduits or channels. Power pulses cause the droplets of ink to be expelled as required from orifices or nozzles at the ends of the channels.
In a thermal ink-jet printer, the power pulse is usually produced by a heater transducer or a resistor, typically associated with one of the channels. Each resistor is individually addressable to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in the associated channel and initially bulges toward the channel orifice followed by collapse of the bubble. The ink within the channel then retracts and separates from the bulging ink thereby forming a droplet moving in a direction away from the channel orifice and towards the recording medium whereupon hitting the recording medium a dot or spot of ink is deposited. The channel is then refilled by capillary action, which, in turn, draws ink from a supply container of liquid ink.
The ink jet printhead may be incorporated into either a carriage type printer, a partial width array type printer, or a page-width type printer. The carriage type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead can be sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage which is reciprocated, at a constant speed, to print one swath of information (equal to the length of a column of nozzles), at a time, on a stationary recording medium, such as paper, fabric, or a transparency. After the swath is printed the paper is stepped a distance equal to the height of the printed swath or a portion thereof, so that the next printed swath is contiguous or overlapping therewith. This procedure is repeated until the entire page is printed. In contrast, the page width printer includes a stationary printhead having a length sufficient to print across the width or length of the recording medium at a time. The recording medium is continually moved past the page width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. A page width ink-jet printer is described, for instance, in U.S. Pat. No. 5,192,959, herein incorporated by reference.
Printers typically print information received from an image output device such as a personal computer. Typically, this received information is in the form of a raster scan image such as a full page bitmap or in the form of an image written in a page description language or a combination thereof. The raster scan image includes a series of scan lines consisting of bits representing pixel information in which each scan line contains information sufficient to print a single line of information across a page in a linear fashion. Printers can print bitmap information as received or can print an image written in the page description language once converted to a bitmap consisting of pixel information.
Various methods and apparatus for printing images with scanning carriage type liquid ink printers have been developed. The following references describe these and other methods and apparatus for liquid ink printing.
In U.S. Pat. No 4,748,453 to Lin et al., a method of depositing spots of liquid ink upon selected pixel centers on a substrate to prevent the flow of liquid ink from one spot to an overlapping adjacent spot by printing a line of information in at least two passes is described. In each pass, spots of liquid ink are deposited in a checkerboard pattern where only diagonally adjacent pixel areas are deposited in the same pass.
U.S. Pat. No 5,349,905 to Taylor et al. describes a method and apparatus for controlling peak power requirements of a printer. The printer incorporates a copy speed feed control for reducing peak power requirements. The speed of the sheet transport system is controlled in accordance with the image density so that high image densities, the speed of the sheet at the printer and/or at the dryer is reduced.
U.S. Pat. No 5,382,101 to Iguchi describes a printer driving apparatus for a dot matrix type printer. A measuring circuit measures the number of print drops and a driving circuit changes the drive timings of the dots of a printhead in correspondence to a print ratio in each print cycle. When high speed printing is not required, the capacity of the power source can be reduced. By reducing the print speed, the printing can be performed by a cheap power source.
U.S. Pat. No 5,610,638 to Courtney describes controlling the printing of an image by a thermal ink jet printer based on an internal temperature of the printer and the density of the printed image. Prior to printing, the temperature of the printhead is estimated and the density of the image is determined from stored print data. Also, based on the temperature and density, the printhead droplet ejection rate is set.